Energy use in Industry – Sustainable Energy – TU Delft

Energy use in Industry – Sustainable Energy – TU Delft


In the previous two lectures, we have had
a look at energy use in transportation and in buildings. However, the largest share of global energy
use is in industry, or in other words making things. There are certain type of industry which require
a lot of energy for making their product. These are known as energy-intensive industries. Industries where the primary energy requirement
is more than 3 percent of the total cost of making the final product are considered energy-intensive. It should be noted that this rather arbitrary
classification refers only to primary industry – that is, industry which use freely available
raw material to form their end-product. Iron and steel is a primary industry since
it uses iron ore available in the earth’s crust to form steel. The automobile industry which uses steel as
a raw material to make cars is a secondary industry. The automobile industry is not considered
to be energy intensive since the energy embodied in the iron and steel is not included while
calculating the energy requirement of automobile manufacturing. The industries where the energy costs are
less than 3 percent of the total product costs are called light industries. These include food and drug processing, textile,
automobile and pulp and paper industries. The steel industry is one of the largest in
the energy-intensive category and forms the backbone of almost every other industry. The annual global steel production stands
at over 1000 million tonnes. Over half of the steel is used in the construction
industry. 16 percent is used to manufacture industrial
equipment, 16 percent for other metal products and the remaining 12 percent in the transportation
industry. Of the total annual steel production, 9 percent
goes into manufacturing cars and other light vehicles while 3 percent is used to manufacture
trucks, ships and other heavy modes of transportation. 12 percent of the steel is used in manufacturing
metal goods such as cabinets and chairs, 3 percent is used in making electrical appliances
like washing machines and 1 percent is used for packaging including milk cans and sterile
food packaging. 13 percent of the steel is used for manufacturing
mechanical machinery while 3 percent is used for electrical industrial equipment. Bars of steel reinforcement along with concrete
as structural reinforcement used in construction, is the widest application of steel in the
world. 14 percent goes into infrastructure such as
bridges, rail tracks and so on, while 42 percent is used as structural steel in the construction
of buildings. The aluminium industry is one of the largest
energy consumers after iron and steel. Annually, around 45 million tonnes of aluminium
is manufactured around the world. Of this, 24 percent is used in the construction
sector, 20 percent goes into making industrial equipment, 29 percent goes into metal product
manufacturing and the largest share, 27 percent, is used in the transport sector. This is because of the relative lightness
of aluminium as a structural material. 18 percent of all aluminium goes into making
car frames, engines and chassis elements. 7 percent is used for making large truck chassis,
and 2 percent is used by trains and the aerospace industry, the latter using aluminium extensively
for making aircraft frames. 7 percent of the aluminium goes into making
electric appliances, 13 percent into making packaging such as soda cans and wrapping foil,
and 9 percent is used for other purposes such as paints and pigments and powder metallurgy. 7 percent of the aluminium is used in making
elements for industrial heating and ventilation. 4 percent is used in electrical equipment
and 9 percent is used in making electrical cabling. 24 percent of all the aluminium is used to
make building elements such as window frames, rain
gutters and pipes. Now that we have seen the importance of steel
and aluminium in our daily life, let us take a look at the processes that make these industries
so energy-intensive. Every year, about 38 exa-joules of energy
is required to manufacture the 1040 million tonnes of steel that is used globally. Iron ore is the raw material that is mined
from the earth to make steel. The ore needs to be purified and treated in
blast furnaces. The blast furnace is a high temperature furnace
where iron ore and coal is fed along with lime and heated with hot air and other fuels. The lime reacts with the impurities which
can be removed from the bottom. This is the most energy-intensive process
in the entire chain. The ore can also be purified through oxidation
and direct reduction. An electric arc furnace is used to reduce
scrap iron for making steel. The molten steel is then cast into slabs,
blooms, or billets, and water-cooled. The majority of steel is cast continuously
although a small fraction is still cast as ingots. The cast steel is coated with a range of metals
such as tin and zinc, heated and rolled into sections, bars, or slabs, and formed into
stock products by extrusion, and other forming techniques. Stock steel is cut, bent, and welded as required
to fabricate its wide range of products. The final fabrication often requires high
temperature processes and hence is also an energy-intensive process. The global production of aluminium uses about
7.6 exajoules per year. Aluminium is mined from bauxite before being
treated with hot caustic soda to form sodium aluminate. Aluminium can also be formed by re-melting
and purifying scrap. The sodium aluminate, or alumina, is dissolved
in a cryolite solution at about 950 degrees Celsius. Graphite electrodes electrolyse the alumina
and molten aluminium is deposited. Due to the high temperatures, electrolysis
is the most energy-intensive step in the manufacture of aluminium. The molten aluminium is cooled and cast into
ingots or slabs. It can also be mixed with different metals
to form alloys. The cast aluminium is then heated to around
500 degrees Celsius before rolling into sheets of the required thickness. The ingot can also be drawn into wires by
extrusion and the cast aluminium can be moulded into the required shape to use as an end-product. Apart from iron and steel, and aluminium,
other industries also produce a vast amount of material annually, consuming an enormous
amount of energy. The annual production of cement currently
stands at around 2800 million tonnes across the world, far greater than the global annual
steel production. Aluminium, being a very light material, stands
at the bottom of this table at 45 million tonnes per year. Now let us look at what these numbers mean
for us at a personal level. The green column shows the amount of material
each of us uses on average every year. Even if you may not have built any new structures
recently, the global construction industry uses a large amount of cement. This means that every year, each of us use
the equivalent of 378 kilograms of cement! The orange column shows the energy used by
these materials on a daily basis. Every day, each of us indirectly consumes
3.75 kilowatt-hours for cement use alone! If you recall the earlier lectures, the human-unit
was equal to 2.9 kilowatt hours. This means that our daily energy use for cement
exceeds the amount of energy we use to feed ourselves! Isn’t that some food for thought?! Let’s go back to our rough estimates. We looked at energy use in transportation
and buildings in the previous lectures. We estimate that the global energy use associated
with all industrial activities covers the rest of this pie-chart and stands at around
54% of the total energy used in the world today. Can renewable energy technologies help bring
these numbers down? How much energy is associated with the production
of renewable energy? We shall look at these questions, and delve
deeper into the world of sustainable energy in the coming weeks.

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